Such dosage-dispensing devices are used in particular for the metering of small quantities of dosage material with high precision into target containers. Such target containers are in many cases set on a balance in order to weigh the quantity of the substance delivered out of the dosage-dispensing device, so that is can subsequently be processed further in accordance with a given purpose. The substance to be dispensed is located for example in a dosage-dispensing unit which is equipped with a metering head.
Dosage-dispensing devices for dry and/or powdery bulk materials, for example color dye powders, belong to the known state of the art and are in current use. For example, a device for dispensing measured doses of material is described in U.S. Pat. No. 5,145,009 to Mheidle (“Mheidle '009”), with a dosage-dispensing unit that has a closable outlet at the underside. The closure element is configured as a cone-shaped valve body whose diameter decreases in the upward direction, which can be moved vertically downwards in order to open the outlet opening, which rotates when in its open position, and which is equipped with means to advance the material towards the outlet opening. The dosage-dispensing unit is further traversed by a drive shaft which at top of the dosage-dispensing unit protrudes from the latter and is coupled to a drive mechanism. By way of a fastening flange at its underside, the dosage-dispensing unit is coupled to a drive unit of the dosage-dispensing device. Several pressure cylinders bear against the cover of the dosage-dispensing unit which by way of their stroke movement allow the outlet opening and thus the delivery rate of the dosage-dispensing unit to be influenced.
The pressure cylinders in this device are arranged on a support which is located above the dosage-dispensing unit, whose position can be adjusted up and down by means of a spindle, and which carries the drive mechanism for the rotatable valve body. A further motor actuates the spindle which engages a rotationally constrained spindle nut which is connected to the support, whereby the support, the pressure cylinders and the drive mechanism with the coupler clutch are moved in the vertical direction.
In the operating position, the adjusting elements of the pressure cylinders are in contact, or nearly in contact, with the cover of the dosage-dispensing unit, so that the adjusting elements are available for the opening of the valve.
The engagement of the coupler clutch and the movement of the valve body are thus accomplished by two different drive systems. In this drive unit, dosage material containers of different heights can be used. In spite of having separate drive systems for the clutch engagement and for the opening movement of the valve body, there is always the danger that dosage material could inadvertently be allowed to escape from the dosage-dispensing unit due to a linear displacement of the valve body during the clutch engagement phase. This can happen for example if the support is set in a position too close to the dosage material container. Furthermore, an inadvertent opening can also occur when a form-locking clutch is used, if the two clutch halves are offset against each other radially or in their angles of rotation and therefore push against each other instead of entering into mutual engagement.
A premature release of substance can be dangerous to the user of the dosage-dispensing device in particular with toxic substances. But also with non-critical substances, an unwanted release may be undesirable. This is annoying in particular if a powder mixture is to be assembled of a plurality of powders, where the individual components of the mixture are dispensed into the same target container from dosage-dispensing units which are set one after another into the drive unit.
Unless a very expensive controller and expensive stepper motors with position transducers are used, the clutch engagement has to be manually controlled and executed. This requires a great deal of attention by the user and a very long setup time in comparison to an automated clutch engagement.
The drive unit described in Meheidle '009 with the spindle-adjustable support and the pressure cylinders is characterized by a very complicated design structure and requires very expensive stepper motors with position transducers. Their position-sensing signals are processed by a microcomputer, and the stepper motors are controlled accordingly by the microcomputer. The requirements placed on the mechanism and the electronic circuitry are very high, as the motors need to stop immediately when the clutch engagement position has been attained. With this drive unit it is also necessary to know at least the height of the installed dosage-dispensing unit and thus the position of the clutch and to enter this height manually in the controller. Alternatively, at least the position of the clutch has to be determined, for example by means of an optical sensor, if a premature opening of the delivery orifice is to be prevented. However, the manual entry may be incorrect and lead to the problems described above. Furthermore, the use of sensors is problematic especially in dosage-dispensing devices because of the risk of contamination, as dosage material can adhere to the sensor elements whereby the sensitivity of the sensor can be compromised.
It is therefore the object of the present invention to create a drive unit of a dosage-dispensing device which is characterized by a simple design and a favorable manufacturing cost and which allows the drive unit to be coupled automatically to a dosage-dispensing unit with the highest possible degree of safety.